Compact electric taxi assembly for installation on an aircraft

ABSTRACT

A electric taxi system (ETS) for an aircraft may comprise drive units mounted coaxially with wheels of the aircraft and dedicated motor control units for the drive units. The motor control units may be operable independently of one another so that a first one of the drive units can be operated at a speed different from an operating speed of a second one of the drive units. Independent operability of the drive units may provide enhanced maneuverability of the aircraft during taxiing.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.12/915,746, filed Oct. 29, 2010.

BACKGROUND OF THE INVENTION

The present invention generally relates to aircraft landing gear. Moreparticularly, the invention relates to landing gear with integratedelectric drive systems to propel an aircraft during taxiing.

A typical aircraft may taxi on to and from runways with thrust forcedeveloped by its engines. A significant amount of fuel may be burned bythe engines during a typical aircraft taxi profile before and after eachflight. In many cases, the main engines may provide more motive forcethan is required to complete a successful taxi profile. In that regard,engine-thrust taxiing may be considered inefficient and may contributeto high fuel costs and ground level emissions.

Aircraft designers have sought a more efficient method for propelling anaircraft during taxiing. Electric taxi systems (ETS) have been proposedto provide higher efficiency. An ETS may be implemented by usingelectrical motors to provide the motive force for aircraft taxiing.While this general ETS concept holds promise for improved efficiency,there are practical application problems that need to be addressed inany successful ETS design. For example, it is desirable that an ETS notdiminish brake capacity and structural strength of wheels of anaircraft. Also, installation of the ETS should not impact normaltake-off and landing procedures or aircraft performance. Additionally,an ETS should not add excessive weight to an aircraft.

As can be seen, there is a need for an ETS which may not adverselyimpact or interact in any way with the aircraft braking system.Additionally there is a need for an ETS which may not interfere withsafe aircraft operation during normal take-off and landing cycles. Also,the ETS system should only minimally impact existing aircraft structuresand weight, (e.g., landing gear, landing gear doors, and wheel wellconfiguration).

SUMMARY OF THE INVENTION

In one aspect of the present invention, an electric taxi system (ETS)for an aircraft may comprise drive units mounted coaxially with wheelsof the aircraft; motor control units for the drive units; and whereinthe motor control units are operable independently of one another sothat a first one of the drive units can be operated at a speed differentfrom an operating speed of a second one of the drive units.

In another aspect of the present invention, a drive unit for an ETS maycomprise a drive motor positioned coaxially with a wheel of an aircraft;a selectively engageable clutch assembly positioned coaxially with thewheel; and wherein the clutch assembly is positioned internally to thewheel.

In still another aspect of the present invention, a method for taxiingan aircraft with an ETS comprising the steps of: producing airflowthrough rotors of wheel-mounted drive motors to pre-cool the drivemotors; and driving the motors to rotate wheels of the aircraft.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an electric taxi system (ETS) inaccordance with an embodiment of the invention;

FIG. 2 is block diagram of the ETS of FIG. 1 in accordance with anembodiment of the invention;

FIG. 3 is a perspective view of a wheel of an aircraft having anattached drive unit in accordance with an embodiment of the invention;

FIG. 4 is a partial sectional view of the wheel and drive unit of FIG. 3in accordance with an embodiment of the invention;

FIG. 5 is an illustration of airflow circuits through the wheel anddrive unit of FIG. 3 in accordance with an embodiment of the invention;

FIG. 6 is an illustration of a fan assembly in accordance with anembodiment of the invention; and

FIG. 7 is a flow chart of a method for taxiing an aircraft with an ETSin accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out the invention. The description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the invention, since the scope of theinvention is best defined by the appended claims.

Various inventive features are described below that can each be usedindependently of one another or in combination with other features.

The present invention generally provides an ETS for an aircraft. The ETSmay employ electric motors mounted directly on axles of landing-gearwheels. The motors may be driven with electric power generated by astarter/generator driven by an auxiliary power unit (APU) of theaircraft.

Referring now to FIG. 1, an exemplary embodiment of an ETS 10 which maybe installed in an aircraft 12 is shown in schematic form. The system 10may comprise electric drive units 14 mounted on axles of wheels 16. Apower feed 18 may carry power from an APU 32 (see FIG. 2) to an ETSpower distribution unit 20. A pilot interface unit 22 may be connectedto the ETS power distribution unit 20 through an interface cable 24.Upon appropriate commands from a pilot, electric power may betransmitted to the electric drive units 14 through an ETS feeder 26.

Referring now to FIG. 2, a block diagram may illustrate someinterconnection features of the ETS 10. The drive units 14 may bemounted directly on outboard ones of the wheels 16. The drive units 14may be controlled with dedicated motor control units 28. The motorcontrol units 28 may be pilot-controlled from the pilot interface unit20. Electric power may be supplied to the motor controllers 28 from astarter/generator 30 driven by the APU 32. Power may be supplied throughconventional bus bars 34, contactors 36 and dedicated AC/DC converters38.

Because each of the drive units 14 may be controlled through dedicatedmotor control units 28, the drive units 14 may be operated independentlyof one another. For example, a left hand one of the drive units 14 mayrotate more slowly that a right hand one of the drive units 14. This mayproduce left turning of the aircraft 12. In other words, the ETS 10 ofthe present invention may be used to steer the aircraft 12 duringtaxiing.

Additionally, a left hand one of the drive units 14 may be rotatedcounterclockwise while a right hand one of the drive units 14 may berotated clockwise. In this operational state, the aircraft 12 may bepropelled in a forward direction even though both the left and righthand drive units 14 may be engaged with outboard ones of the wheels 16of the aircraft 12.

The drive units 14 may also be controlled to produce reverse movement ofthe aircraft 12. In that context, the drive units 14 may beadvantageously controlled so that reverse motion of the aircraft 12 isstopped by regenerative braking. By using controlled regenerativebraking, the aircraft 12 may be decelerated slowly so that fuel in itstanks does not shift rearward. This may preclude a potential problemassociated with reverse movement of aircraft, i.e., a center of gravityof the aircraft shifting rearward if fuel shifts rearward. Suchundesirable fuel shifting may cause tilting of the aircraft 12 with anose wheel lifted from the ground and a tail section resting on theground.

Referring now to FIG. 3, an outboard one of the wheels 16 is shown. Forpurposes of clarity, the wheel 16 is shown without a tire. The wheel 16may comprise a hub 16-1 and rims 16-2. In an exemplary embodiment of theinvention, the wheel 16 may have a split-hub configuration. The wheel 16may have a split line 16-3 along which the wheel 16 may be separated forpurposes of installing and removing tires. The drive unit 14 may bemounted adjacent an outboard one of the rims 16-2 and coaxially with thewheel 16. Advantageously, the drive unit 14 may have an outside diameterthat is no larger than an outside diameter of the rim 16-2.

Referring now to FIG. 4, a partial cross-sectional view of the wheel 16may illustrate various inventive features of the drive unit 14. Thedrive unit 14 may comprise a drive motor 14-1 supported concentricallywith a wheel axle 40. In that regard, the drive motor 14-1 may beconsidered to be a wheel-mounted drive motor. Advantageously, the drivemotor 14-1 may be a Segmented ElectroMagnetic Array (SEMA) motor. Rotors14-1-1 of the drive motor 14-1 may be adapted to rotate around the wheelaxle 40. The rotors 14-1-1 may be connected to drive a clutch assembly14-2. The clutch assembly 14-2 may be selectively engageable with thewheel 16. In other words, the wheel 16 may be driven by the drive motor14-1 when the clutch assembly 14-2 may be engaged. Conversely, when theclutch assembly 14-2 may be disengaged, the wheel 16 and the motor rotor14-1-1 may be rotatable independently of one another.

In an exemplary embodiment the wheel 16 may have a first hub portion16-1-1 and a second hub portion 16-1-2. The split line 16-3 may define alocation at which the two hub portions 16-1-1 and 16-1-2 may beseparated. In FIG. 4, the hub portion 16-1-1 may be shown at a left sideof the split line 16-3 and the hub portion 16-1-2 may be shown at aright side of the split line 16-3. A brake assembly 42 may beincorporated into the hub portion 16-1-1. The clutch assembly 14-2 maybe located in the hub portion 16-1-2. The motor 14-1 may be locatedoutside of the hub portion 16-1-2 and adjacent the rim 16-2.

The relative positions of the motor 14-1, the brake assembly 42 and theclutch assembly 14-2 may be advantageous for a number of reasons. Firstof all, the brake assembly 42 may be located in the wheel 16 at alocation that is consistent with conventional locations of brakeassemblies in many conventional wheel of existing aircraft.Consequently, such conventional wheels may be retro-fitted for ETSoperation without reconfiguration of their brake assemblies.

Secondly, conventional aircraft wheels typically have a hollow chamberin their outboard hub portion. In the present embodiment of theinvention, the clutch assembly 14-2 may be internally positioned in thisotherwise hollow hub portion (i.e., the hub portion 16-1-2). Thisarrangement provides for a reduced axial projection of the drive unit14. In other words, the drive unit 14 may extend only a limited axialdistance beyond the rim 16-2. In this regard, it may be advantageous toposition the drives units 14 in outboard ones of the wheels 16 as shownin FIG. 2. When the wheels 16 are retracted after takeoff, the driveunits 14 may be oriented in a downward position. As a consequence, anaircraft may be easily retrofitted with the inventive ETS because only alimited modification to landing gear doors (not shown) may be needed toaccommodate minimally extending drive units 14. If drive units wereinstalled on inboard wheels, an extensive fuselage reconfiguration mightbe required to accommodate drive units when landing gear is stowed.

An additional advantage of the present embodiment may be that the motor14-1 may have a diameter larger than an interior of the hub portion16-1-2. Increasing diameter of a SEMA motor may result in increasedtorque availability.

It may also be noted that the drive unit 14 may include a blower motor14-3 which may be operated independently from the drive motor 14-1.Advantageously, the blower motor 14-3 may be a SEMA motor.

Referring now to FIG. 5, a partial sectional view of the drive unit 14and the wheel 16 may illustrate cooling features of an exemplaryembodiment of the invention. A series of arrows may represent a motorcooling airflow circuit 6. A series of arrows may represent a brakecooling airflow circuit 48.

The blower motor 14-3 may be operated at a desired rotational speedirrespective of the speed at which the drive motor 14-1 may be operated.Consequently, a positive airflow may be induced along the motor coolingairflow circuit 46. The airflow circuit 46 may pass between elements ofthe rotor 14-1-1 of the drive motor 14-1. As a result of positivecooling, the drive motor 14-1 may be operated with a high torque outputeven when it may have a low rotational speed. Indeed, the drive motor14-1 may be safely operated in an overcurrent condition for extendedtime periods because of cooling produced with the blower motor 14-3.This feature may allow for use of a relatively small and readilystowable drive motor, even though there may be high torque requirementsassociated with moving the aircraft 12. Referring now to FIG. 6, it maybe seen that a fan assembly 50 may be attached to and adapted to rotatewith the rotor 14-1-1. Fan blades 50-1 may be circumferentiallydistributed around the fan assembly 50. Rotation of the fan assembly 50may induce airflow along the motor cooling airflow circuit 46 and/or thebrake cooling airflow circuit 48.

In an exemplary embodiment, the drive unit 14 may be constructed suchthat the fan assembly 50 may selectively induce airflow only in themotor cooling airflow circuit 46 or in both the motor cooling airflowcircuit 46 and the brake cooling airflow circuit 48.

Typically, the brake assembly 42 may become hot as a result of brakingduring landing. In some aircraft, the brake assembly 42 may beconstructed with carbon brake elements (not shown). Heat generatedduring landing may raise the temperature of the carbon elements above athermal threshold. At such high temperatures, the carbon brake elementsmay be deleteriously oxidized if cooling air is blown over the brakeassembly 42. But, in spite of the desirability of avoiding applicationof cooling air at potential oxidation temperatures, it is necessary toreduce the temperature of the brake assembly 42 before the aircraft mayproceed to a subsequent take-off. In other words, an aircraft needs tohave cool brakes before initiating a takeoff roll so that, in the eventof a need to perform a rejected take-off, the brakes will performeffectively.

The drive unit 14 may accommodate these operational brake coolingrequirements. Airflow through the brake cooling airflow circuit 48 maybe selectively blocked with an air block 52 (shown in FIG. 5). Whenbrake temperature is at or above potential oxidation temperature (i.e.,after landing), the air block 52 may be closed. The drive units 14 maypropel the aircraft 12 on the tarmac while the air block 52 may remainclosed. With the air block 52 closed, the fan blades 50-1 may induceairflow only in the motor cooling airflow circuit 46. In other word,even though the drive motor 14-1 may be running to move the aircraft 12,the carbon elements of the brake assembly 42 may not be subjected toinduced airflow that may cause potentially deleterious oxidation.

Brake temperature may drop as a consequence of natural heat radiationand/or convection. The air block 52 may be opened after braketemperature has fallen below the potential oxidation level. The fanblades 50-1 may then induce airflow through the brake cooling airflowcircuit 48 so that the brake assembly 42 may be positively cooled inpreparation for a subsequent take-off.

In an exemplary embodiment of the drive unit 14, the air block 52 may beinterconnected with the clutch assembly 14-2 such that disengagement ofthe clutch assembly may result in opening of the air block 52; and sothat engagement of the clutch assembly 14-2 may result in closure of theair block 52. Thus, when the aircraft may stop (e.g., at a gate), theclutch assembly 14-2 may disengage the drive motor 14-1 from the wheel16 and the drive motor 14-1 may then be operated at a high speed. Highspeed operation of the drive motor 14-1 may propel the fan assembly 50at a corresponding high speed. Induced cooling airflow mayadvantageously pass through the brake assembly 42 (along the circuit 48)thereby cooling the brake assembly.

Referring back now to FIG. 3, it may be seen that a shroud 16-4 may beattached to the wheel 16 and may overlie a portion of the drive unit 14.The shroud 16-4 may be adapted to rotate at the same rotational speed asthe wheel 16. The shroud 16-3 may be useful to protect against tiredamage during high speed taxiing turns of the aircraft 12. In some highspeed turns, a tire (not shown) may deflect so that its sidewall (notshown) may protrude beyond the rim 16-2 of the wheel 16. Moreover, theprotruding portion of sidewall may project below the rim 16-2. In thisevent, the sidewall may come into contact with the shroud 16-4. Contactbetween the sidewall and the drive unit 14 may be precluded by presenceof the shroud 16-4. Without such a feature, the tire might be damagedbecause the drive motor 14-1 may rotate at a speed different from thatof the wheel 16. Contact between the tire and the motor 14-1 may resultis damage to the tire.

Referring now to FIG. 7, a flow chart 700 may illustrate an exemplarymethod which may be employed to taxi an aircraft with ETS. In a step702, a blower motor may be started (e.g., a pilot may operate the pilotinterface unit 22 to start the blower motor 14-3 of the drive unit 14 toinitiate cooling airflow across the rotor 14-1-1 of the drive motor 14-1to pre-cool the drive motor). In a step 704, the drive unit may beengaged with the wheels by engaging the clutch assembly (e.g., theclutch assembly 14-2 may be engaged so that rotation of the rotors14-1-1 may impart rotation to the wheels 16). In a step 706, current maybe applied to drive units to move the aircraft (e.g., the pilot mayoperate the pilot interface unit 22 to apply electrical power from themotor control units 28 to the drive units 14 to produce desired rotationof the wheel 16 and movement of the aircraft in either a forward orreverse direction). In a step 708, the aircraft may be taxied to atake-off position. In a step 710, the drive units may be disengaged fromthe wheels (e.g., the pilot may operate the pilot interface unit 22 todisengage the clutch assembly 14-2). In a step 712 takeoff of theaircraft may be performed in a conventional manner.

In a step 714, landing of the aircraft may be performed in aconventional manner (e.g., landing may be performed with the clutchassembly 14-2 disengaged so that the wheels 16 do not produce rotationof the drive motors 14-1). In a step 716, the drive unit may be engagedwith the wheels after the aircraft has stopped on a landing runway(e.g., the pilot may operate the pilot interface unit 22 to engage theclutch assembly 14-2). In a step 718, current may be applied to driveunits to move the aircraft (e.g., the pilot may operate the pilotinterface unit 22 to apply electrical power from the motor control units28 to the drive units 14 to produce desired rotation of the wheels 16and movement of the aircraft). In a step 720, the aircraft may be taxiedto a gate. In a step 722, the clutch assembly may be disengaged. In astep 724, the drive motor may be operated to cool the brake assemblies(e.g., the drive motor 14-1 may be operated at a high speed so that thefan assembly 50 may produce cooling air flow through the brakeassemblies 42).

It should be understood, of course, that the foregoing relates toexemplary embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

We claim:
 1. A drive unit for an electric taxi system (ETS) comprising:a drive motor positioned coaxially with a wheel of an aircraft, thewheel coupled with a brake assembly having carbon brake elements; aclutch assembly selectively engageable to drive the wheel with the drivemotor and adapted to be positioned coaxially with and internally to thewheel; a fan assembly for producing cooling air flow through the carbonbrake elements in the brake assembly; and an air block configured toblock air flow from the fan assembly to the carbon brake elements in thebrake assembly in response to a portion of the brake elements having atemperature at or above a potential oxidation temperature of the carbonbrake elements.
 2. The drive unit of claim 1 wherein the drive motor isa Segmented ElectroMagnetic Array (SEMA) motor.
 3. The drive unit ofclaim 1 further comprising: a blower motor; wherein the blower motor ispositioned coaxially with the drive motor; and wherein the blower motoris operable at a rotational speed different from the drive motor.
 4. Thedrive unit of claim 3 wherein the blower motor provides airflow througha rotor of the drive motor so that the drive motor is operable in anovercurrent state.
 5. The drive unit of claim 1 further, wherein the fanassembly is attached to a rotor of the drive motor.
 6. The drive unit ofclaim 5 wherein the drive motor is operable when the clutch assembly isdisengaged so that the fan assembly can produce the cooling airflow tothe brake assembly while the aircraft is stopped.
 7. The drive unit ofclaim 1 wherein the drive motor has an outside diameter smaller than anoutside diameter of a rim of the wheel.
 8. The drive unit of claim 7wherein the drive motor has an outside diameter larger than an insidediameter of a hub of the wheel.
 9. The drive unit of claim 1 wherein thedrive motor is positioned in a shroud that is attached to the wheel sothat the drive motor is precluded from damaging a tire of the aircraft.10. The drive unit of claim 1, wherein the air block is configured toselectively block air flow from the fan assembly to the brake assemblyduring operation of the fan assembly.